Heat exchangers for EGR systems formed by a stack of planar conduits where each of these planar conduits is formed by two steel sheets die-cut and welded to one another are known in the state of the art. In turn, inside each planar conduit there are corrugated sheets increasing the turbulence of the gas to be cooled and improving convection and therefore the transfer of heat to the coolant liquid circulating outside these conduits.
Planar conduits formed by die-cut and welded sheets having an embossment formed by embossing which favours the formation of channels or cavities between consecutive conduits for allowing the passage of the coolant liquid.
In such heat exchangers, the stack of conduits is housed in a shell which is what contains the coolant liquid. The shell is a structure which in turn has its inlet and outlet for the passage of the coolant liquid which removes the heat extracted from the hot gas. The volume of liquid in the shell comprises the volume between the planar conduits as well as the liquid between the shell and the stack of conduits where the latter is significant and increases the total weight of the device by a high percentage.
The experience of a person skilled in the art in the design of such exchangers cannot be extrapolated to other manufacturing methods and materials such as extruded aluminium. Not only are they materials with very different thermal conductivity and expansion coefficients, but the manufacturing and welding techniques are completely different and do not allow using the configurations used with stainless steel parts.
A type of aluminium plate called clad is known in the state of the art. Such aluminium plate in turn has a layer of aluminium with a melting point lower than the rest of the aluminium of the same plate on at least one of its surfaces. Throughout the description and the claims, when the term clad is used it will refer to such aluminium plate comprising a layer of aluminium with a melting point lower than the rest of the aluminium of the same plate on at least one of its surfaces.
The advantage of such plate is that it allows attachments with parts the surface of which contacts the surface with aluminium with a reduced melting point (reduced being understood as lower) by introducing them into an oven. The attachment process consists of subjecting the parts to be attached, including the clad plate, to a temperature greater than the melting temperature of the aluminium of reduced melting point but lower than the melting temperature of the rest of the aluminium.
At this temperature the aluminium of reduced melting temperature melts, attaching the contacting surfaces and the aluminium of higher melting temperature maintains structural integrity.
In the case in which it is necessary, for example, to attach two perpendicularly intersecting plates, in the state of the art the clad plate is elongated in a perpendicularly emerging segment so that the surface with the aluminium of reduced melting temperature of said segment contacts the other plate. The attachment is produced because the surface of this perpendicular segment having a lower melting temperature is parallel to the surface to be attached and contacts it. The passage through the oven for raising the temperature melts the aluminium contacting the part to be attached in particular, and it is assured that both plates, located perpendicular to one another, are welded.
The present invention provides a heat exchanger of a simple construction, lacking a shell, based on using extruded aluminium profiles the attachment of which is assured using clad plates used differently to how it is used in the state of the art. Other technical solutions combined with the foregoing are described in the following sections of the description.